Ovens following the present invention and having linear sources of visible and infra-red radiant energy are disclosed and described in U.S. Pat. No. 5,036,179 and U.S. patent application Ser. No. 07/738,207 which are incorporated herein by reference. These ovens provide high-speed, high-quality cooking and baking of food items by impinging high-intensity visible, near-visible, and infrared radiations onto a food item. The ovens cook the food items within the short periods of time normally found in microwave cooking while maintaining the browning of infrared cooking and the quality of conduction-convection cooking. When food is exposed to a sufficiently intense source of visible, near-visible, and infrared radiation, the food absorbs low levels of visible and near-visible radiation, thereby allowing the energy to penetrate the foodstuff and heat it deeply. The longer infrared radiation does not penetrate deeply but acts as an effective browning agent.
Ordinarily, the source of the visible, near-visible and infrared radiation for this invention is in excess of two elongated quartz-halogen tungsten lamps, or equivalent means such as quartz arc lamps. Typical quartz-halogen lamps of this type operate at 3000 degrees Kelvin and convert electrical energy into black body radiation having a range of wavelengths from 0.4 .mu.m to 4.5 .mu.m with a peak intensity at 0.965 .mu.m. Each lamp can generally provide about between 1.5 and 2 kW of radiant energy with a significant portion of the energy in the visible light spectrum.
The ovens can use a plurality of these lamps or an array of several lamps either operated in unison or selectively operated in varying combinations as necessary for the particular food item sought to be cooked. These radiation sources are ordinarily positioned above and below the food item. The walls of the surrounding food chamber are preferably made from highly reflective surfaces. The visible and infrared waves from the radiation sources impinge directly on the food item and are also reflected off the reflected surfaces and onto the food item from many angles. This reflecting action improves uniformity of cooking.
The intensity of radiant energy received by an object decreases with the increase in distance between the object and the radiant energy source. Despite the improved uniformity of cooking provided by the reflective interior surfaces of the oven, the areas of the food item that are positioned directly above or below the radiation sources receive more direct energy and therefore cook more quickly than their surrounding areas.
FIGS. 1A and 1B show an end view and a longitudinal side view, respectively, of a single linear radiation source 100 and further show the distributions of light intensity measured at the surface of a food item positioned underneath the radiation source. As shown in both figures, the regions of the food item which are positioned directly below the light source are exposed to the maximum intensity received by the food item, while the surrounding areas are exposed to significantly lower intensities.
FIG. 2A shows a lamp configuration under which a food item 104 is cooked under an array of elongate radiation sources 100 that are shorter than the length of the food item and that are arranged in parallel. The food item is cooked to the desired degree in the regions of the food item that are close to the lamps, designated by shading in FIG. 2B. The unshaded regions remain uncooked or undercooked.
Rotating the food item relative to the stationary radiation sources also yields a non-uniformly cooked end product. FIG. 3A shows a circular food surface 104, such as a pizza, positioned underneath a single radiation source 100a having a length l. The radiation source is parallel to and shorter than diameter d of the pizza. Referring to FIG. 3B, when the pizza is rotated about its center C, the radiation source cooks a circular region AA having diameter equal to the length l of the radiation source 100a. Moreover, cooked portion AA is itself non-uniformly cooked: the regions that are closer to the center C spend more time under the radiation source and therefore are cooked more thoroughly than those regions that are further away from it.
As shown in FIGS. 4A and 4B, positioning a single source 100b parallel to a diameter d of the rotating pizza will cook only an annular path BB, leaving the remainder of the pizza uncooked.
Combining the concepts described with respect to FIGS. 3B and 4B partially solves the problem of non-uniform cooking. FIG. 5A shows five equally spaced radiation sources 100c, 100d, 100e fixed over a pizza 104 which is positioned on a rotating rack (not shown). The sources are equal in length, and their length l is less than the diameter d of the pizza 104. The center source 110c lies above the diameter of the pizza, and the outer radiation sources are positioned parallel to it.
When the pizza is rotated about the center C, the energy generated by radiation sources 100d and 100e creates partially cooked annular paths similar to region BB in FIG. 4B. These paths are also exposed by the center source 100c, although their exposure time is minimal as explained with respect to FIG. 3B.
Designing an oven having radiation sources that extend beyond the outer boundaries of the food location in the oven would allow uniform cooking of the food region even where the sources are arranged as in FIG. 5A. However, there are limits to the size of radiation sources that can be manufactured for use in ovens of the present type, making it often impractical to utilize radiation sources that are longer than the area of food sought to be cooked. To attempt to do so would unnecessarily limit the size of the food items which could be cooked using combined visible and infra-red radiation. A lamp configuration is therefore needed that will provide uniform cooking even where the size of the cooking surface exceeds the dimensions of the lamps.